Interference between the elastic phonon scatterings by bound electrons and point defects

The interference between the elastic phonon scatterings by bound electrons and donor point defects in semiconductors has been studied in two cases. First when the electron and the donor point defect belong to the same site in the approximation of isolated impurity. Second when they are at different sites assuming the impurity atoms to be distributed around the origin with a mean-square radius Rl2. In both cases contribution of such interference to the relaxation rate τ−1 becomes vanishingly small i.e. Matthiessen's rule stands justified.